In response to the trend toward high integration of integrated circuits in semiconductor devices, DRAMs require smaller memory cells and larger memory capacity. With respect to this requirement, metal-insulator-metal (MIM) capacitors have been given attention. MIM capacitors employ a high-k dielectric material such as strontium titanate (SrTiO3) as a material of an insulating film (dielectric film).
As for the method for forming SrTiO3 films for DRAM capacitors, conventionally, there is widely used an atomic layer deposition (ALD) method using Sr(DPM)2 serving as an Sr material, Ti(O-iPr)4 or Ti(O-iPr)2(DPM)2 serving as a Ti material, and an O3 gas, an O2 gas, H2O or O2 plasma serving as an oxidizing agent (e.g., J. H. Lee et al. “Plasma enhanced atomic layer deposition of SrTiO3 thin films with Sr(tmhd)2 and Ti(i-OPr)4”
J. Vac. Sci. Technol. A20(5), September/October 2002 (Non-patent document 1).
However, Sr(DPM)2 used as an Sr material has a low vapor pressure and is hardly adsorbed on the surface of a substrate. Accordingly, it has disadvantages of low throughput and bad coverage due to its low film forming rate. Further, Sr(DPM)2 should be heated to a temperature exceeding 200° C. to be provided in a gas phase. Further, Sr(DPM)2 requires the use of a heat-resistant material for piping system or the like, thus incurring an increase in equipment costs. Further, Sr(DPM)2 is not readily adsorbed on the substrate surface, as mentioned above, is easily decomposed in a gas phase, and is hardly oxidized by an oxidizing agent after adsorption, so that it is difficult to form an oxide film. Accordingly, it is difficult to determine optimal supply conditions of Sr material or oxidizing agent for ALD.